Digital electronic setworks control for sawmills



April 30, 1968 3,380,495

DIGITAL ELECTRONIC SETWORKS CONTROL FOR SAWMILLS Filed Dec. 30, 1965 c. w. WESTON, JR

4 Sheets-Sheet 1 Hal COMPUTER ELECTRICAL TRANSDUCER lllllvll 5 a m S m YS m mmm &M L D G R R A T L D ER S V 08 mmmw W l w u %Mm J 3 N n J W m y A B u R 9 mm m 0 uFWMwL U L I m L mw z s "MU E L 3 w S 4 7 o- I PIII IIIL 8 I m H I Y 4 WH 4 L 1 SME u L E WM 5 WW f w R & E u u S M L E R INVENTOR. CLEMENT WALKER WESTON, JR.

HQ 2 MMML ATTORNEY.

April 30, 1968 c. w. wzsrorq, JR

DIGITAL ELECTRONIC SETWORKS CONTROL POP. SAWMILL-S Filed Dec. ISO, 1965 4 Sheets-Sheet 2 BRAKE SET SHAFT "sToP" "DECEL" FIG. 3

(IJMPRESSED AIR SUPPLY AIR MOTOR TO WAVE SHAPER April 30, 1968 c. w. WESTON, JR

DIGITAL ELECTRONIC SETWORKS CONTROL FOR SAWMILL-S Filed Dec. 30, 1965 4 Sheets-Shae: 5

I N lll l i .L 5.31m w mm P QR April 30, 1968 c. w. WESTON, JR

DIGITAL ELECTRONIC SETWORKS CONTROL FOR SAWMILLS Filed Dec. 30, 1965 4 Sheets-Sheet 4 FIG. 5

rrrrr a)? 114-4111 United States Patent This invention relates to sawmill systems and more particularly to an electronically controlled sawmill setworks.

The function of a sawmill setworks is to control the indexing action of a log so that it can be moved in relation to a saw blade a finite predetermined distance with a high degree of respeatable accuracy. On a sawmill carriage, this action is always considered in the question of advancing the head blocks or knees of the carriage toward the saw line. For example, ifit is desired to cut a board with the net measure thickness of 1%", the knees would have to be moved by that amount plus an additional amount which is approximately equal to the saw kerf so as to makeup for that amount of the wood which is lost as sawdust.

Heretofore, a large variety of mechanisms have been employed to perform this function. The oldest types now in use consist of a ratchet and pawl mechanism attached to a lever with the indexing being operated by a man who might be located on or off of the carriage. Other verisons include power assist devices which permit easy and faster setting of the head blocks and, more recently, it has been customary to allow the carriage operator to control the index action remotely, that is, without the presence of a rider on the carriage.

Various types of setworks have been utilized to accomplish this objective. By far the largest number of these have depended on their having a source of power on the carriage such as an electric motor, air motor, hydraulic motor, or hydraulic cylinder, etc. for moving the head blocks, plus a measuring device for controlling the amount of movement. Some form of clutch or other reset mechanism is included which must operate in order to permit a second or repetitive index to be made.

Two types of apparatus have been generally utilized. In one, the measuring device consists of a relatively light signal setworks which is usually equipped with a number of limit switches. In operation, a small clutch is engaged at the start of a set and as the head blocks begin to move forward under power, the signal arm is drawn ahead towards a preselected limit switch until it strikes that switch. This provides the stop signal for the power system. It is then necessary for the small clutch to disengage and the measuring arm or device will be returned to its original position by the action of a spring or gravity. In the second general type, which might be referred to as a master measuring system, the measuring is actually done by the process of limiting, either mechanically or electrically, the maximum movement of a mechanism which is bound mechanically into the power train which turns the set shaft. Like the signal type, this mechanism must be released and reset to zero following each set; which implies the use of some kind of clutch system.

It is an object of the present invention, therefore, to provide an electronically controlled setworks for automatically advancing the head blocks of a sawmill to a specified position.

It is another object of the present invention to remotely control the setting of the head blocks of a sawmill to position the log in proper relation to the saw for cutting a desired thickness of lumber.

It is still another object of the present invention to 3,380,495 Patented Apr. 30, 1968 provide an electronically controlled setworks for sawmills wherein the indexing action is controlled by high speed digital counting apparatus.

It is yet another object of the present invention to provide a remotely controlled sawmill setworks in which the power train is reduced to a substantial degree.

It is still another object of the present invention to employ digital computer techniques to accurately control the distances set of head block knees on a sawmill carriage.

Briefly, the subject invention comprises a prime mover located on the carriage, having command signals applied thereto in response to output signals from a digital computer which in turn receives a pulse input from a transducer which is sensitive to the rotational movement of the set shaft of the sawmill carriage. The transducer produces a series of pulses, the number of which is indicative of the linear movement of the head blocks. By encoding the digital computer with information as to the desired thickness of lumber to be cut, the computer Will provide a first output signal in accordance with a first predetermined number of pulses counted to decelerate the setworks movement prior to the final desired setting and will provide a second output signal in accordance with a second predetermined number of pulses counted to stop the setworks at the desired setting.

Other objects and advantages will become apparent from a reading of the following detailed description when considered in conjunction with the accompanying drawings, in which:

FIGURE 1 is a perspective view of a portion of a sawmill carriage including a setworks;

FIGURE 2 is a block diagram illustrative of the preferred embodiment of the subject invention;

FIGURE 3 is a combined electrical and mechanical schematic diagram illustrative of the control apparatus utilized in combination with the subject invention;

FIGURE 4 is an electrical schematic diagram illustrative of the electronic digital computer apparatus utilized in connection with the subject invention;

FIGURE 5 is an electrical schematic diagram of one type of electrical circuitry utilized with the subject invention; and

FIGURE 6 is an electrical wiring diagram of an alternate means for encoding the electronic digital computer illustrated in FIGURE 4.

A setworks, whether manually or power operated, normally applies power to the head blocks through a shaft hereinafter referred toas a set shaft. Spur pinions are keyed to the set shaft and engage gear racks fixed to the head blocks. Rotary motion of the set shaft is translated into linear motion of the head blocks. The log is held in position against the head blocks by clamping devices called dogs. By advancing the head blocks, the setworks positions the log in relation to the saw. When a log has been completely cut, the head blocks are retracted away from the saw so as to receive the next log.

Referring now to the present invention, FIGURE 1 illustrates a portion of a sawmill carriage with a setworks mounted thereon. In detail, the sawmill carriage 10 is comprised of a generally rectangular base member to which is attached a plurality of wheels 11 so that the carriage may roll back and forth along a track or guide, not shown. Head block bases 12 are mounted on the carriage 10 so as to substantially span the entire width thereof. Head blocks 13 are slidably mounted on the head block bases 12 in a generally vertical position and are adapted to move back and forth across the bases. Dogs 14 are located on the head blocks and are adapted to clamp a log, not shown, positioned on the head block bases 12 and resting against the head blocks 13. The present invention utilizes a prime mover 16 mounted on of a sprocket drive 18. The head blocks 13 are driven by the sprocket drive 18 by means of a respective pinion gear 19 coupled to the rack 20. The prime mover 16 then is used for driving the head blocks 13 through the set shaft 17. An air operated brake means 21 is located on the set shaft 17 so as to retard the translational movement of the head blocks 13 upon command by exerting a restraining force on the rotational movement of the set shaft 17.

FIGURE 2 is a block diagram of apparatus which is adapted to control the movement of the head blocks 13 shown in FIGURE 1 by selectively controlling the operation of the prime mover 16 and the brake means 21. A set button 22 located on a chassis 25 is coupled to a first or ,fast latching relay 23 which in turn is coupled to a second or slow latching relay 24. The chassis 25 is preferably located on the operators stand commonly referred to as a sawyers stand, not shown. The fast latching relay 23 has two leads 26 and 27 tied to terminals 28 and 29, respectively, for purposes to be explained more fully subsequently. The second latching relay 24 which may be referred to as a slow latching relay has two output lead's 31 and 32 coupled to terminals 33 and 34, respectively. Both latching relays 23 and 24 are electrically coupled to relay drivers 35 by means of leads 36 and 37, coupled to terminals 81 and 80, respectively.

A digital computer 38 shown comprising a digital counter 39 and diode AND gates 41 is coupled to a wave shaper circuit 43 by means of the circuit lead 44. The diode AND gates 41 are coupled to the relay drivers 35 by means of leads 40 and 50. The pulse shaper unit is coupled to an electrical transducer 42 by means of the circuit lead 45. The electrical transducer 42 is shown mounted on the prime mover 16 and is adapted to be responsive to a gear 46 having a predetermined number of teeth mounted on the main shaft 47 of the prime mover 16. The electrical transducer is adapted to produce an electrical pulse each time a tooth of the gear 46 passes under the transducer head.

A set selector switch 48 is coupled to the digital counter 39 by means of the circuit lead 49. The set selector switch 48 acts as an encoder for the computer 38 and is the means by which the sawyer selects the desired thicknesses of lumber to be cut by the sawmill. A reed relay 51 is adapted to be coupled to the digital counter 39 through set selector switch 48. The reed relay 51 is coupled to the slow latching relay 24 by means of circuit lead 52 and is adapted to be activated thereby.

Briefly, the operation of the digital setworks control shown in FIGURE 2 operates as follows. The sawyer, after having selected a set or thickness by means of the set selector switch 48, then briefiy pushes the set button 22 which sequentially activates the latching relays 23 and 24 and the reed relay 51, such that the fast latching relay 23 energizes first which in turn activates slow latching relay 24 and reed relay 51. Reed relay 51 is energized only for the moment of time required for slow latching relay 24 to operate, which operation de-energizes coil 104 of reed relay 51. The latching relays 23 and 24 transmit command signals to the prime mover 16 and the brake 21, deactivating the brake and starting the prime mover to drive the head blocks 13 in a forward direction. As the reed relay 51 is activated, the digital counter 39 is selectively SET and RESET as determined by the selector switch 48 so as to be in a ready condition for counting pulses when applied thereto. As the prime mover 16 turns, the electrical transducer 42 generates a predetermined number of electrical pulses per revolution of the gear 46. Since the shaft 47 is coupled to the set shaft 17 of the setworks by means of a sprocket drive 18, the number of pulses produced by the electrical transducer 42 is proportional to the linear translation of the head blocks 13 coupled to the set shaft 17 by means of the rack 20 and pinion gear 19.

The electrical pulses from the transducer 42 are fed to a pulse shaper circuit 43 which transforms the pulses into square waves of equal frequency, and standard amplitude. The output of the pulse shaper 43 comprising the square waves are fed to the digital counter 39 where a counting operation takes place such that after a first predetermined number of pulses have been counted, a first output signal is translated by the diode AND gates 41 to the fast latching relay 23 which then sends a decelerate brake command signal to the brake 21 and removes a forward prime mover command signal from the prime mover 16 causing the movement of the head blocks 13 to slow down in preparation for a complete stop. When the desired head block movement has occurred, the digital computer 39 will have counted a second predetermined number of pulses as determined by the selector switch 48, at which time a second output signal will be translated by the diode AND gates 41 to the slow latching relay 24 which transmits a stop brake command signal to the brake means 21 and removes another forward prime mover command signal from the prime mover 16, bringing the motion of the head blocks 13 to a sudden stop. The system has now completed one cycle of operation and is instantly ready for another.

Proceeding now to a more detailed description of the subject invention, FIGURE 3 is an electro-mechanical schematic diagram of the means by which the prime mover 16 and the brake 21 is controlled by means of the fast latching relay 23 and the slow latching relay 24. First, considering the mechanical features, the prime mover 16 and the brake 21 are comprised of an air motor and an air actuated clutch, respectively, adapted to be powered from a compressed air supply 60 by means of the air line 61. A main valve 62 is connected between the line 61 and the compressed air supply 60 for providing a master control valve for the system. The air line 61 is coupled to the air motor 16 by three electrically operated solenoid valves 63, 64 and 65. The valves 63 and 64 are used to control air flow to the prime mover 16 so as to provide two forward speeds. The valve 63 is designated slow forward valve and includes a speed control valve 66 located between the valve and the prime mover 16. The second forward speed valve 64 is designated the fast forward valve. The third valve 65 is designated reverse and is utilized to drive the prime mover 16 in a reverse direction, after the sawing cycle described above has been completed.

The brake 21 is connected to the set shaft 17 and is coupled to the, air line 61 by means of two electrically operated solenoid valves 69 and 70. The first valve 69 is designated a decelerate valve and additionally hasa check valve 71 and a control valve 72 connected in the line connected to the air line 61. The second valve 70 is designated the stop valve. 7

Each electrically operated solenoid associated with the solenoid valves 63, 64, 65, 70 and 71 has one terminal thereof returned to a point of reference potential illustrated and hereinafter referred to as ground. The opposite terminal of the solenoid for the slow forward valve 63 is connected to terminal 33 on the sawyers stand 25 by means of circuit lead 73. The corresponding terminal of the solenoid associated with the fast forward valve 64 is connected to terminal 29 by means of circuit lead 74. The solenoid of the reverse valve 65 is coupled to the reverse switch 75 by means of circuit lead 76. The reverse switch 75 is adapted to couple a v. AC potential applied across terminals 106 and 107 to the solenoid of the reverse valve 65 through the switch 78 and the fuse '79. Regarding the solenoids associated with the brake valves, the solenoid for the decelerate valve 69 is coupled to terminal 28 by means of circuit lead 77 and the solenoid for valve 70 is connected to terminal 34 by means of circuit lead 78.

The electrical circuitry utilized to operate the aforementioned solenoid valves is embodied in the latching relays 23 and 24. Relay 23 is comprised of two relay coils 82 and 83 and two sets of relay contacts 84 and 85. Latching relay 24 is also similar to latching relay 23 and also comprises two relay coils 87 and 88 and two sets of relay contacts 89 and 90. These relays are so constructed that energizing one coil for about 20 milliseconds will operate the relay to a first position which will be maintained when power is removed. When power is applied momentarily to the other coil, the relay will move its second position, where it will be latched even though de-energized. A source of negative potential is adapted to be connected to the sawyers stand 25 by means of terminal 91 and a source of positive potential adapted to be coupled to terminal 92. Terminal 93 is connected to ground.

The relays 24 and 23 are interconnected such that relay 23 is energized first which in turn energizes relay 24. The circuitry disclosed shows the set push button 22 coupled between ground and the relay contacts 90. One terminal of the relay coil 82 is coupled to relay contact 94 while the opposite end thereof is connected to terminal 91 such that a momentary closure of switch 22 will energize relay 23 to a first latched position causing relay contacts 84 and 85 to switch to the opposite terminal from that shown in FIGURE 3. The electrical circuitry shown in FIGURE 3 further discloses the electrical connection of the fast latching relay 23 and the slow latching relay 24 to the respective solenoid operated valves associated with the air motor 16 and the brake 21. With respect to relay 23, one terminal of relay coil 82 is connected to terminal 91 while the opposite terminal is connected to terminal 94 of relay contacts 90. A common connection i also made between relay terminal 94 and relay terminal 95 of relay contacts 85. Relay terminal 96 of relay contacts 90 is connected to one side of the set button switch 22 which has its other terminal connected to ground. The relay coil 87 of relay 24 has one terminal connected to terminal 91 while the opposite terminal is connected to terminal 97 of relay contacts 85 forming a part of the fast latching relay 23.

The second relay coil 83 forming a part of the fast latching relay 23 has one terminal connected to terminal 91 of the sawyers stand 25 while the opposite end is connected to terminal 81. The second relay coil 88 forming a part of the slow latching relay 24 has one terminal connected to terminal 91 while the opposite terminal is connected to terminal 80.

The set of relay contacts 84 of the fast latching relay 23 has terminal 98 connected to terminal 92 to which is applied a potential of 120 v. AC. Terminal 99 is coupled to the solenoid of the decelerate valve 69 through leads 26 and 77 tied together at terminal 28. Relay terminal 100 is coupled to the solenoid of the fast forward valve 64 "by means of circuit leads 27 and 74 tied together at terminal 29. Similarly, the set of relay contacts 89 forming a part of the slow latching relay 24 has relay terminal 101 connected to terminal 92 which is also common to relay terminal 98. Relay terminal 102 is coupled to the solenoid of the stop valve 70 by means of circuit leads 32 and 78 tied together at terminal 34. Relay terminal 103 is coupled to the solenoid of the slow forward valve 63 by means of circuit leads 31 and 73 tied together at terminal 33. Also contained in the sawyers stand 25 is the reed relay 51 which has its relay coil 104 coupled across terminal 91 and relay terminal 97 of relay contacts 85. The armature 105 of relay 51 is connected to ground while the normally open contact 106 is coupled to terminal 54 by means of circuit lead 55.

The circuitry illustrated in FIGURE 3 is shown when the setworks is in the stop condition. At this time, the stop valve 70 and the decelerate valve 69 are activated through the relay contacts 89 of the slow latching relay 24 and relay contacts 84 of the fast latching relay 23. When the set button 22 is depressed firmly, relay coil 82 is energized through relay contacts 90. When this occurs, relay contacts 84 and 85 will switch such that relay terminals 95 and 97, and 98 and 100 will make contact.

At that instant, the solenoid of the decelerate valve 69 is de-energized and the solenoid of the fast forward" valve 64 is energized supplying air to the air motor 16. The relay coil 87 is next energize-d through the set button 22 and the relay contacts and 85. Also, the reed relay 51 is energized by means of the relay coil 104 causing the armature to make contact with the nor mally open contact 106. The function of the reed relay 51 is to clear and preset the digital counter 39 by selectively grounding certain terminals as will be explained subsequently.

As the slow latching relay 24 is energized, the relay contacts 90 will open, thereby locking out the set button 22 but at the same time relay terminals 101 and 103 of relay contacts 89 will make contact. This de-energizes the solenoid of the stop valve 70 and energizes the solenoid of the slow forward valve .63 thereby supplying additional air to the prime mover 16 from the line 61. Also, when the slow latching relay 24 energizes as described, the reed relay 51 will be tie-energized due to the opening of the relay contacts 90. The relay 24, as mentioned above, is a latching relay, and it will maintain its selected position when the energizing voltage is removed; however, the reed relay 51 requires continuous voltage to maintain its energized position and therefore the contact 106 and the armature 105 will only make contact momentarily.

Referring now to FIGURE 4, there is shown in greater detail the circuitry comprising the computer 38 shown in FIGURE 2. Additionally, the gear 46 mounted to the main shaft of the prime mover (air motor) 16 is shown as well as the wave shaper circuit 43. The gear 46 is selected in the embodiment disclosed to have a predetermined number of teeth which, when sensed by the electrical transducer 42, will produce 256 pulses per inch of travel of the head blocks 13 shown in FIGURE 1. Although the gear 46 is shown connected to the shaft 47, it is shown by way of example only and is not meant to be considered in a limiting sense. For instance, the gear might also be mounted on the set shaft 17. Regarding the transducer 42, it is comprised of a magnetic pick-up producing alternating current pulses each time a gear tooth passes. While a magnetic pickup is illustrated, other suitable pick-up devices might be utilized such as an AC tachometer as well as a rotation sensing mercury switch, or an electro-optical transducer might be utilized when desired. The only requirement on the transducer 42 is that it must respond to the rotation of either the prime mover shaft 47 or the set shaft 17 with a periodic electrical wave being produced whose frequency is a direct function of the angular velocity thereof. The pulses generated by the transducer 42 are fed to the wave shaper circuit 43 by means of a cable 45. The Wave shaper circuit 43 is illustrated in more detail in FIGURE 5 and will be explained subsequently. The output signal of the wave shaper 43 comprises square Waves of standardized amplitude having the same frequency as the input pulses fed thereto and are fed into the digital counter circuit 39.

The digital counter 39 is comprised of 11 flip-flop circuits FFI through FFll with an additional flip-flop FFC coupled between the fourth and fifth flip-flops F1 4 and FFS. Each of the flip-flop circuits are shown in block diagrammatic form since such circuitry is Well known to those skilled in the art and is superfluous to this description. Each flip-flop moreover includes an input terminal C, a SET S and a RESET R terminal as well as two output terminals 1 and 0. The fiip-fiops shown are designed around PNP transistors and will change state when a positive going pulse is fed to its count input C.

For purposes of explanation, standard logic levels are employed such that a logic ZERO is equal to 0 volts and a logic ONE is equal to 6 volts. When a flip-flop is SET, its 1 output will be at 6 volts (ONE) while its output will be at 0 volts (ZERO). When a flip-flop is RESET, the 1 output will be at 0 volts (ZERO) and the 0 output will be at 6 volts (ONE). For example, initially, it the 1 output of a flip-flop is in a ZERO logic state, a positive going pulse fed to its input C, the 1 output will switch to a ONE logic state.

It will be observed that the first four flip-flops, hereinafter referred to simply as PP, FFl-FF4 are coupled together such that each 1 output is coupled to the following input C. Also the respective terminal S of PF1-- PF4 are commonly connected to position 1 of a three position rotary switch 108 while the respective terminal R is commonly connected to positions 2 and 3 of one section of the switch.

The 1 output of FF4, moreover, is coupled to the C input of PFC. The input terminal C1 of PFC is returned to ground while the input 5 is commonly coupled to positions 1 and 2 of the second section of switch 108. Position 3 of the second section of switch 108 is connected to the R input of PFC. The anode of diode 110 is commonly connected to the 1 output of PP4 and the C input of PFC while the cathode is coupled to the common connection of resistor 112 and the cathode of diode 111. The resistor 112 is adapted to be coupled to a 12 volt supply voltage while the cathode of diode 111 is coupled to a -6 volt supply voltage. A third diode 113 is coupled between the 1 output of PFC and the C input of FPS. A common connection is also made to the diode 110, the resistor 112 and the diode 111.

FPS through PF11 are coupled together in cascade such that each 0 output is connected to the following C input. The S and R inputs are selectively connected to the set selector switch 48 which is illustrated for the sake of an example as seven separate toggle switches respectively coupled to the R and S inputs of FF5FP11.

A first AND gate 41a, comprising diodes 112 through 118, is coupled to FPS-PF11 such that the cathodes of diodes 112-118 are coupled together in parallel to circuit lead 50. The anodes of diodes 113, 114, 116, 117 and 118 are connected to the 0 outputs of FPS, FF6, PP7, FP9, PP10 and PF11, respectively; however, the anode of diode 115 is connected to the 1 output of FF8. The purpose for this connection will be subsequently explained. A second AND circuit 41b, comprising diodes 122 through 128, are coupled to FPS-PF11 such that their cathode electrodes are respectively connected to circuit lead 40. The anode electrode of diodes 122-128 are respectively connected to the common connection of the 0 output of the preceding FF and the C input to the following PP.

The leads 40 and 50 are coupled to relay driver circuits 35 which are transistor amplifiers for activating the slow latching relay 24 and the fast latching relay 23. The relay driver circuits 35 are comprised of two transistors 130 and 131 coupled together such that transistor 130 acts as an emitter follower and transistor 131 acts as a power amplifier.

The embodiment of the digital counter 39 shown in FIGURE 4 is described with respect to a configuration in which the transducer 42 produces 256 pulses per inch of travel of the head blocks. It should be observed that this is shown by way of example only and is not meant to be interpreted in a limiting sense since the embodiment shown would have to be modified slightly should a gear 46 having different number of teeth be utilized.

The principle of operation of the counter 39* is to count a predetermined number of pulses for a particular set commanded by the sawyer. For example: if 32 pulses correspond to A; inch movement of the head blocks, the counter would count down through FPl-FFS since each flip-flop acts as a +2 circuit. PFC is normally inoperative and is used for adding a small increment of travel and will be described more fully subsequently. The output of the counter 39 is translated by means of the diode gates 41a and 41b. The AND gate 41a is used for a preliminary slow-down and will provide a first output signal for decelerating the setworks while the AND gate 41b will provide a second output signal which will bring the setworks to a complete stop.

The following table is illustrative of the counting sequence as it relates to movement of the head blocks 13:

Inches FFl corresponds to FF2 corresponds to FP3 corresponds to A PF4 corresponds to FPS corresponds to PF6 corresponds to A), FF7 corresponds to ,4 FPS corresponds to FF9 corresponds to 1 FF10 corresponds to 2 PF11 corresponds to 4 It is to be noted that FFl-FF4 are wired as an up counter. They are followed by PFC, the functionof which is to serve as a control flip-flop for lengthening a measured increment of travel at will. The last seven flipfiops PPS through PF11 are wired as a down counter, so called since every selected increment of travel will be completed with a full counter so that a first deceleration output signal can be generated at a predetermined distance away from the complete travel of the setworks desired. In the subject embodiment, this is desired at /2 in. from the completion of any desired set (thickness of cut). The position of rotary switch 108 is shown in the normal position 2. The wiper of both sections is connected to the preset bus 49.

The flip-flop units FF1PF11 are adapted to assume their SET or RESET state when one or the other of the inputs S or R are grounded or driven to a logical zero state by means of the reed relay 51. Thus, the preset bus 49 is so arranged that when the sawyer initiates a set, meaning initiating a cycle of operation of the sawmill by means of set switch 22, the reed relay 51 energizes momentarily, grounding the PRESET bus 49 through terminal 54 causing all of flip-flops PF1-PP11 and FPC to assume their commanded conditions according to the positions of the set selector switch 48 and encoding switch 108. The capacitor 135 is used to filter any possible noise which might appear 011 the bus 49 and have a tendency to change the state of the flip flops during a counting operation. The resistor 134 acts as a current limiting device designed to protect the reed relay contacts 105 and 106 shown in FIGURE 3 against the discharge of capacitor 135. The resistor 134 shown coupled to 12 volts is used in order to permit the bus to return rapidly to -l2 volts condition for a counting operation.

The operation of FF1 through PFC is as follows: actuation of the set button 22 shown in FIGURE 3 closes the reed relay 51 when the slow latching relay 24 energizes. The reed relay contacts are closed and then immediately released by opening of the relay contacts of relay 24. The momentary energization of the reed relay 51 moreover grounds the PRESET bus 49 and with the switch 108 being in the #2 position, PP1 through FF4 will all be RESET, i.e., their 1 outputs will be at 0 volts (Zero). PFC, however, will be SET, i.e., its 1 outputs will be at -6 volts (ONE). On the first positive pulse from the wave shaper 43, FF1 will reverse states so that its 1 output switches to 6 volts (ONE). The next pulse from the transducer will drive FFl back to 0 volts (Zero) and the input to FF2 will see the positive going pulse and itself will switch. Thus, the binary count will progress through the first four stages until FF4 has flipped to its logic O-NE state and is just about to be driven back to its ZERO state. During this interval, the input C of FPS will be clamped to 6 volts by the action of resistor 112 and the diode 111. When PF4 is driven back to its ZERO or RESET state, a positive pulse will appear at the anode of the diode 110 whose cathode is at 6 volts. The positive pulse will thus appear at the count input of FFS due to the fact that the C1 input of PFC is grounded and the S input thereof has been SET. FFC in this condition will not be responsive to the output of FF4 and therefore is blocked out of the circuit. It should be pointed out that FFC has absolutely no effect on the pulse count when it starts out in the SET condition.

Considering the operation of FFl-FFC when the switch 108 is moved to position #3, FF1 through FF4 will all be RESET as before. Thus 16 pulses will be required to cause these units to apply a count input to FFC. However, in this instance, FFC has been RESET and its 1 output will be at a logic ZERO level. It may be seen that the count input of FFS will thus be held at volts. When the 16th pulse from the wave shaper 43 appears, the 1 output of FF4 will be switched from a logic ONE to a logic ZERO state. Because it is already being held at 0 volts (ZERO), the count input of FF5 will not recognize this pulse; however, the input of PFC will recognize the pulse and will be forced to its SET state where its '1 output will flip to its ONE state. The gating will then. be seen to be in a state where the next inch carry signal will drive FPS and the count will then proceed. In this manner, 16 pulses (those necessary to create an output at FF4) will be waste-d and the counter obliged to deliver an extra inch regardless of the selected width of lumber to be cut as selected by the switch 48. FFC then is utilized to add an extra discrete element to any desired cut at will. Stated another way, an extra 5 inch is added to the desired cut while the switch 108 is in position #3.

Where it is desirable to make the out come out slightly less than the desired thickness, the swtich 108 is placed in the #1 position. In this condition, the preset bus 49 will be connected to FF1 through FFC at the respective S input terminal. Thus, presetting the 1 outputs to -6 volts (ONE). When the operator calls for a specific set, the first pulse from the transducer 42 will switch FFl through FFS because the first input pulse will cause the 1 output to go positive (ONE to ZERO); thereby flipping all four flip-flops with the first input pulse. FFC, however, will remain inoperative. It can be clearly seen that under this condition, the counter will think" that the head blocks have traveled A of an inch upon receipt of the first pulse. Thus, the desired thickness cut by the sawmill will be completed short by this amount, i.e., A inch.

Considering now FF5FF 11, they are coupled together in a down counter configuration so that two output signals are provided, one a predetermined number of pulses prior to the second output signal. The selector switch 48 which in the embodiment shown in FIGURE 4 is comprised of seven single pole double throw (SPDT) toggle switches, the purpose of which is to encode the down counter FPS- FF11 so as to provide output signals in response to the desired width of lumber to be cut. The toggle switches are shown merely for the sake of explanation and a preferred embodiment of the set selector switch 48 is shown in FIGURE 6 and will be discussed subsequently. As illustrated in FIGURE 4, all of the flip-flops except FF9 (1 inch flip-flop) are shown in the RESET position, i.e., reed relay 51 will ground the S terminal. With this setting, FFl through FF4 will deliver one pulse per 16th inch to the down counter section. The first such pulse from FF4 will flip FFS from its ONE state to its ZERO state and will carry all the way into FF9. The next pulse to FF5 will restore it to its original RESET state. Because FF9 has its 0 output at 0 volts, the first pulse is stopped at this point and does not appear in the final two flip-flops FF and FFll. Following the initial pulse from FF4, the count will progress in normal binary fashion. If one follows the counting procedure, watching the voltage conditions on the diode AND gate 41a, which can be termed the deceleration gate, it will be found that a time exists at which the 0 outputs of FFS, FF6, FF7, FF9, FF10 and FF11 will be at 6 volts as well as the 1 output of FF8. Prior to reaching this condition, there has always been one or more of these outputs at 0 volts or ground. Thus, the input to the emitter follower amplifier has been clamped at ground potential. The instant that the cathode junction of the diodes 112 through 117 is lifted from ground, i.e., when 6 volts appears at all the abovementioned outputs, base current will flow in the emitter follower 130 rendering it conductive which in turn drives amplifier 131 into conduction. When transistor 131 becomes conductive, the relay coil 83 of the latch relay 23, shown in FIGURE 3, will be energized due to the fact that terminal 81 is virtually at ground potential. Energizing of relay coil 83 will latch relay 23 such that relay terminals 98 and 99 make contact. This de-energizes the solenoid of the fast forward valve 64 coupled to the prime mover 16 and energizes the solenoid of the decelerate valve 69 activating the brake 21. The deceleration gate 41a produces the output signal necessary to trigger the emitter follower 130 until the next pulse is transferred into the down counter from FF4. By this time, the mechanical latch has been secured by relay 83.

Following the deceleration or first output signal from the AND gate 41a, the count will continue to progress until the 0 outputs of FFS through FF1'1 have all reached a condition of 6 volts. At that instant, the clamp on the cathode bus of the diodes 122 through 128 of the second AND gate 41b, which might be termed the STOP gate, will fall to a negative voltage causing the transistor amplifier 130 connected to circuit lead 40 to conduct and at the same time triggering the amplifier 131 into conduction. Terminal 80, shown in FIGURE 3, is virtually placed at ground potential and the relay coil 88 of the slow latching relay 24 is energized causing relay terminals 101 and 102 to make contact. This de-energizes the solenoid of the slow forward valve 63 which completely shuts off power to the prime mover 16 and energizes the solenoid of the stop valve 70 which further delivers air to the brake 21 causing it to stop the head block travel very rapidly. Since the prime mover is no longer rotating, no additional pulses will be sent to the counter 39 from the transducer 42 and the coil 88 will remain energized even though latching has taken place. The circuit is designed to maintain this load indefinitely, however, and no harm will result from this condition.

Referring now to FIGURE 5, there is shown a schematic diagram of the wave shaper circuit 43 shown in block diagrammatic form in FIGURES 2 and 4. The wave shaper circuit 43 is comprised of a transistorized clipper amplifier including transistor 137 coupled to a Schmitt trigger circuit including transistors 138 and 139. A Schmitt trigger circuit is well known to those skilled in the art and is commonly referred to as a squaring circuit. The transistor amplifier 137 is a conventional amplifier circuit of the grounded emitter type. The diodes 143 and 144 are coupled across the input terminal 140 and 141 for clipping both the positive and negative halves of the input signal applied thereacross. Terminal 140- is adapted to be coupled to the transducer 142 by means of the cable 45. The clipped input signal applied to the base of transistor 137 is amplified and coupled to the base of transistor 138 which is the input to the Schmitt trigger circuit. This signal is clamped between 12 and 6 volts by means of the diode 146 for proper operation of the Schmitt trigger. The output is in the form of a square wave which appears at the collector of transistor 139. This output signal is coupled to the input of the digital counter by means of circuit lead 44 coupled to the terminal 147. For a further discussion of the Schmitt trigger circuit, attention is directed to the Department of the Army Technical Manual, TM11-690, entitled The Basic Theory and Application of Transistors, at page 208.

FIGURE 6 is a schematic diagram of the preferred embodiment of the set selector switch 48 shown in block diagrammatic form in FIGURE 2. It comprises a three deck rotary selector switch 48' which is mechanically coupled together. The reset bus 49 coupled to the reed relay 51 is used to selectively SET and RESET the counter circuit 39 at the beginning of each set cycle of the setworks. By rotating the selector switch 48 a desired width of lumber to be out can be selected. The switch 48 encodes the up counter circuits FF6 through FF10. A direct connection is made from the preset bus 49 to the S input of FPS and to the R input of FFll. The FFS flip-flop corresponds to the inch travel of the head blocks, FF6 corresponds to a inch travel, FF7 corresponds to ,5, inch travel, etc. As shown, the preset bus 49 is coupled through the P terminal of deck 1 such that the R input is connected to the C terminal while the S terminal is commonly connected to the A, B, D, E, F and G terminals. Regarding the FF7, the S terminal is connected to the M, K and I terminals, while the R terminal is commonly connected to the O, N, L and J terminals of deck 1. Considering deck 2 of the rotary switch 48, the S terminal of FF8 is commonly con nected to the A and F terminals and the R input terminal of FF8 is commonly connected to the B, C, D, E and G terminals. The terminals 0, N, M, K and I of deck 2 are commonly connected to the S input terminal of FF9. The L and I terminals of deck 2 are commonly connected to the R input terminal of FF9. Only A; of deck 3 of rotary switch 48 is utilized and it is used to connect the preset bus 49 to the flip-flop 10. The R input terminal of FF10 is commonly connected to the A, B, C, E and F terminals, whereas the S input terminal is connected to the D and G terminals. It should be pointed out, however, that any desired combinations can be mechanized, depending on how the switch 48' is wired.

The operation of the rotary switch 48' is essentially the same as selectively setting each toggle switch shown with the encoder switch 48 of FIGURE 4 with the exception that the connection to the proper R and S input terminal is done automatically by a selection of the width to be cut. The 4" flip-flop FFll was directly connected from its R terminal to the preset bus 49, so as to RESET it on every set of the head blocks because none of the sets required the flip-flop to be SET. Since inch was required on all sets, the SET side of flip-flop 5 was also directly connected to the .preset bus 49. Thus, for example, for the measured head block movement of 1%; inches, the rotary switch would be in its second position, ordering SET on inch (FF 5) and 1 inch flip-flops (F1 9) while order RESET on 4 inch (FF7), A inch (FPS) and 2 inches (F1 10).

What has been described therefore is a digitally controlled sawmill setworks which once having selected the desired cut or set and initiating the action of the setworks by means of the set 'button 22, the stop and decelerate solenoid-operated valves 70 and 69 will be deactivated, releasing the brake 21. The fast forward and slow forward solenoid-operated valve 64 and 63 will be sequentially activated to drive the prime mover 16 in the forward direction. The rotation of the set shaft 17 moves the head blocks 13. As the head blocks move the transducer 42 generates a predetermined number of pulses per inch of travel. These pulses are converted to square waves and fed into a digital counter circuit which is encoded by means of the SET selector switch 48. As the digital counter circuit 39 counts the pulses applied to its input, the AND gate 41:: translates a first output signal a predetermined number of pulses inch of travel) less than the desired count for a selected travel of the head blocks 13. The first output signal latches relay 23 such that the fast forward solenoid valve 64 is deactivated and the decelerate valve 69 is energized slowing the movement of the setworks at some time prior to the full selected travel. When the counter circuit 39 counts a second predetermined numher of pulses signifying a full count as selected by the encoder switch 48, a second output signal is gated out 12 by means of the AND gate 41b latching the relay 24 which deactivates the slow forward solenoid valve 63 and energizes the stop solenoid valve 70 bringing the setworks to an immediate halt.

While there has been shown and described what is at present considered to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. For example, the digital control setworks described may be powered by an electric or hydraulic motor as well as the pneumatic motor means shown and described. Secondly, as noted above, the electrical transducer may be selectively positioned as desired as long as movement of the head blocks can be converted into an electrical signal which is indicative of the linear travel thereof. Also a continuous deceleration of the head blocks can be provided when desired. It is not desired, therefore, that the invention be limited to those specific arrangements shown and described but it is to be understood that all equivalents, alterations and modifications within the spirit and Scope of the present invention are herein meant to be included.

I claim as my invention:

1. A digital electronically controlled setworks for automatically advancing the head blocks of a sawmill carriage to a selected position for cutting a predetermined width of board comprising in combination:

prime mover means, having command signals applied thereto, coupled to the head blocks of said sawmill carriage for selectively advancing and retracting said head blocks in response to said command signals;

transducer means coupled to said prime mover means and generating a signal in the form of a pulse train the number of pulses of which is proportional to the advancement of said head blocks on said carriage; electronic digital counter means coupled to said transducer means and being responsive to said pulse train to provide a first and a second output signal after a first and a second predetermined number of pulses of said pulse train have been counted; reset circuit means coupled to said digital counter means for selectively setting and resetting said counter means in accordance with a control signal; selector means, for determining a desired width of board to be cut by said sawmill, coupled to said digital counter means for encoding said counter means to produce said first output signal when said first predetermined number of pulses are counted and said second output signal when said second predetermined number of pulses are counted;

switch means, coupled between said counter means,

said prime mover means and also to said reset circuit and being responsive to said first output signal to transmit a decelerate command signal to said prime mover means and being responsive to said second output signal to transmit a stop command signal to said prime mover means as determined by the time delay occurring between said first and said second predetermined number of pulses counted by said digital counter means; and

control means coupled to said switch means applying a set signal thereto whereupon said switch means removes staid decelerate and said stop command signal from said prime mover means and transmits a first and a second forward speed command signal to said prime mover means and transmits said control signal to said reset circuit for selectively setting and resetting said digital counter means.

2. A digital electronically controlled setworks for automatically advancing the head blocks coupled to the set shaft of a sawmill carriage to a selected position for cutting a predetermined width of lumber comprising in combination:

prime mover means, having prime mover command signals applied thereto, coupled to the set shaft of said 13 sawmill carriage for selectively advancing and retracting said head blocks in response to said prime mover command signals; brake means, having at least one command signal applied thereto, coupled to said set shaft of said sawmill carriage for decelerating said head blocks in response to said at least one command signal;

transducer means responsive to the rotational movement of said set shaft generating an electrical signal in the form of a pulse train the number of pulses of which are proportional to the advancement of said head blocks on said carriage;

electronic computer means coupled to said transducer means being responsive to count the pulses of said pulse train to provide an output signal in accordance with said advancement of said head blocks; reset circuit means coupled to said computer means for selectively setting and resetting said computer means in accordance with a control signal applied thereto;

selector means, determining said predetermined width of lumber to be cut by said sawmill, coupled to said computer means for encoding said computer means to produce said output signal;

switch means coupled between said computer, said prime mover means, said brake means, and said reset circuit means and being responsive to said output signal to transmit said at least one command signal to said brake means; and

control means, for starting said setworks, coupled to said switch means applying a set signal thereto which removes said at least one command signal from said brake means and applies prime mover command signals to said prime mover means and applies said control signal to said reset circuit.

3. A digital electronically controlled setworks for automatically advancing the head blocks coupled to the set shaft of a sawmill carriage to a selected position for cutting a predetermined width of lumber comprising in combination prime mover means, having prime mover command signals applied thereto, coupled to the set shaft of said sawmill carriage for selectively advancing and retracting said head blocks in response to said prime mover command signals;

brake means, having brake command signals applied thereto, coupled to said set shaft of said sawmill carriage for selectively decelerating and stopping said head blocks in response to said brake command signals;

transducer means responsive to the rotational movement of said set shaft generating an electrical signal in the form of a pulse train the number of pulses of which are proportional to the advancement of said head blocks on said carriage;

an electronic digital counter coupled to said transducer means, being responsive to said pulse train to provide a first and a second output signal after a first and second predetermined number of pulses have been counted;

reset circuit means coupled to said digital counter means for selectively setting and resetting said counter means in accordance with a control signal applied thereto;

selector means, determining said predetermined width of lumber to be cut by said sawmill, coupled to said counter means for encoding said counter to produce a first output signal when said first predetermined number of pulses have been counted and said second output signal when said second-predetermined number of pulses have been counted;

switch means coupled between said counter means, said prime mover means, said brake means, and said reset circuit means and being responsive to said first output signal to transmit a decelerate brake command signal to said brake means and being responsive to said second output signal to transmit a stop brake command signal to said brake means; and

control means for starting said setworks coupled to said switch means applying a set signal thereto whereupon said switch means removes said decelerate andsaid stop brake command signals from said brake means and applies a first and second forward speed prime mover command signal to said prime mover means and applies said control signal to said reset circuit means coupled to said digital counter means.

4. The invention as defined in claim 3 wherein said prime mover means comprises: a fluid motor, powered from a fluid power source, coupled to said set shaft and additionally includes a plurality of electrically operated solenoid valves coupled to said fluid motor for controlling the fluid flow from said fluid power source to said motor, electrical circuit means coupling a first and a second solenoid valve of said plurality of electrically operated solenoid valves to said switch means such that said first solenoid valve is responsive to said first forward speed prime mover command signal and said second solenoid valve is responsive to said second forward speed prime mover command signal, and electrical circuit means coupling a third solenoid valve of said plurality of electrically operated solenoid valves to said control means for receiving a reverse speed command signal.

5. The invention as defined in claim 3, wherein said brake means comprises: a fluid actuated clutch coupled to the set shaft of said carriage, a plurality of electrically operated solenoid valves, fiuid circuit means coupling said plurality of solenoid valves to said clutch, electrical circuit means coupling a first solenoid valve of said plurality of electrically operated solenoid valves to said switch means being responsive to said decelerate brake command signal to effect a slowing down of the movement of said head blocks, and electrical circuit means coupling a second solenoid valve of said plurality of electrically operated solenoid valves to said switch means responsive to said stop brake command signal to effect a full stop of the movement of said head blocks.

6. The invention as defined in claim 3, .wherein said transducer means comprises: an electrical pick-up device selectively mounted on said setworks so as to be responsive to the rotational movement of said set shaft and producing a preselected number of pulses per revolution of said set shaft.

7. Apparatus as defined by claim 3, wherein said transducer means comprises: a gear, having a selected number of teeth, mounted on said prime mover means, and a magnetic pick-up transducer located in the vicinity of said gear and being responsive to the rotational movement thereof and producing a preselected number of electrical pulses equal in number to the number of said gear teeth.

8. Apparatus as defined by claim 3, and additionally including a pulse forming circuit coupled between said transducer means and said digital counter means for shaping the pulses of said pulse train into square waves suitable for driving said digital counter means.

9. The invention as defined by claim 3, wherein said electronic digital counter means comprises: a plurality of electrical binary circuits connected in cascade relationship, each said electrical binary circuit including an input, an output terminal, a set and a reset terminal; circuit means coupling said transducer means to the input terminal of the first of said plurality of binary circuits; circuit means coupling said encoding means selectively to the set and reset terminals of said binary circuits so that said binary circuits count a preset number of pulses for a particular width of lumber selected by said encoder means; an AND gate circuit comprising a plurality of diode means coupled to said plurality of binary circuits for feeding said first output signal to said switch means, and another AND gate coupled to said binary counter circuits and comprising a plurality of diode means for feeding said second output signal to said counter means.

10. The invention as defined by claim 3, wherein said digital counter means comprises: a first plurality of electrical binary counter circuits coupled together in cascade relationship and adapted to be operated an an up counter circuit; a second plurality of binary electrical counter circuits coupled together in cascade relationship and adapted to be operated as a down counter, and still another electrical binary counter circuit coupling said first plurality of counter circuits to said second plurality of counter circuits, each binary counter circuit having an input, an output, a set and a reset terminal, circuit means for selectively coupling said encoder means to the set and reset terminals of said down counter, and switch means coupled to said up counter and said still another binary counter by means of the set and reset terminals thereof for selectively varying an incremental number of pulses applied to said down counter, a first AND circuit coupled to said down counter for feeding out said first output signal to said switch means, and a second AND circuit coupled to said down counter coupling said second output signal a predetermined time later to said switch means.

11. The invention as defined by claim 3, wherein said electronic digital counter means comprises: an up counter comprising a plurality of flip-flop circuits coupled together in cascade circuit relationship, a down counter circuit comprising a plurality of flip-'flop circuits coupled together in cascade circuit relationship, another flip-flop circuit coupling said down counter to said up counter, all of said flip-flop circuits each including an input, an output, a set, and a reset terminal, circuit means, for coupling the input terminal of the first flip-flop circuit of said up counter to said transducer means, circuit means selectively coupling said encoding means to the set and reset terminals of said down counter programming said down counter to produce said first output signal a predetermined count before said up counter has achieved a full count at which time said second output signal is produced, first gating means coupled to said down counter for translating said first output signal to said switch means, second gating means coupled to said down counter for translating said second output signal to said switch means, and circuit means coupling said reset circuit to said down counter, said up counter and said another flip-flop circuit to apply a reference potential thereto for selectively setting and resetting all of said flip-flop circuits when said control signal is applied.

12. The invention as defined by claim 11 and additionally including amplifier means coupling said first and said second gating means to said switch means.

13. The invention as defined by claim 3', wherein said reset circuit comprises: electrical relay means coupled between said switch means and said digital counter means, being activated by said switch means and including at least one set of contacts which is coupled between said counter means and a point of reference potential for momentarily applying a reference potential to said counter means thereby selectively setting and resetting said counter means so as to be responsive to a new pulse train from said transducer means.

14. The invention as defined by claim 3, wherein said switch means comprises: a first relay circuit including a first latching relay having .a first relay coil and a second relay coil, circuit means coupling said first relay coil to said control means for receiving said set signal therefrom to switch said first latching relay from a first state to a second state, said second relay coil being coupled .to said counter means for receiving said first output signal to switch said first latching relay from said second state to said first state, and a second relay circuit including a second latching relay having a third and a fourth relay coil, said third relay coil being coupled to said first relay circuit for switching said second latching relay from a first state to a second state, said fourth relay coil being coupled to said counter means for receiving said second output signal to switch said second latching relay from said second state to said first state, and circuit means coupling said second relay circuit to said reset circuit for activating said reset circuit momentarily when said econd latching relay switches from said first state to said second state.

15. Apparatus as defined by claim 3, wherein said switch means comprises a first and a second latching relay, each having a first and a second relay coil for selectively switching said relays between a first and a second stable operating state, circuit means coupling said first relay coil of said first latching relay to said control means, circuit means coupling said second relay coil of said first latching relay to said counter means, circuit means coupling said first relay coil of said second latching relay to said first latching relay, circuit means coupling said second relay coil of said second latching relay to said counter means, and circuit means coupling said second latching relay to said reset circuit activating said reset circuit when said first and said second latching relay sequentially switch from said first stable state to said second stable state.

16. The invention as defined by claim 3, wherein said switch means comprises a first and a second latching relay circuit, circuit means coupling said first latching relay circuit to said control means, said counter means, and said second latching relay circuit and being responsive to said set signal from said control means to latch in a first position thereby removing said decelerate command signal and transmitting a first forward command signal to said prime mover means and being responsive to said first output signal from said digital counter means for latching said first latching relay to a second position for transmitting a decelerate command signal to said prime mover means and removing said first forward command signal applied thereto; and circuit means coupling said second latching relay circuit to said first latching relay circuit, said counter means, and said reset circuit means being responsive to the operating state of said first latching relay circuit to latch in a first position when said first latching relay latches in its respective first position, removing said stop command signal and applying said second forward speed command signal to said prime mover means and being responsive to said second output signal from said counter means to latch in :a second position removing said second forward command signal and applying said stop command signal to said prime mover means.

References Cited UNITED STATES PATENTS 2,767,363 10/1963 Chubb 143--120.1 2,969,094 1/ 1961 Johnson 143-1201 2,983,290 5/ 1961 Thedick 143-120.1 3,298,408 1/ 1967 Jordan 143--'l15 WILLIAM W. DYER, 1a., Primary Examiner.

W. D. BRAY, Assistant Examiner. 

1. A DIGITAL ELECTRONICALLY CONTROLLED SETWORKS FOR AUTOMATICALLY ADVANCING THE HEAD BLOCKS OF A SAWMILL CARRIAGE TO A SELECTED POSITION FOR CUTTING A PREDETERMINED WIDTH OF BOARD COMPRISING IN COMBINATION: PRIME MOVER MEANS, HAVING COMMAND SIGNALS APPLIED THERETO, COUPLED TO THE HEAD BLOCKS OF SAID SAWMILL CARRIAGE FOR SELECTIVELY ADVANCING AND RETRACTING SAID HEAD BLOCKS IN RESPONSE TO SAID COMMAND SIGNALS; TRANSDUCER MEANS COUPLED TO SAID PRIME MOVER MEANS AND GENERATING A SIGNAL IN THE FORM OF A PULSE TRAIN THE NUMBER OF PULSES OF WHICH IS PROPORTIONAL TO THE ADVANCEMENT OF SAID HEAD BLOCKS ON SAID CARRIAGE; ELECTRONIC DIGITAL COUNTER MEANS COUPLED TO SAID TRANSDUCER MEANS AND BEING RESPONSIVE TO SAID PULSE TRAIN TO PROVIDE A FIRST AND A SECOND OUTPUT SIGNAL AFTER A FIRST AND A SECOND PREDETERMINED NUMBER OF PULSES OF SAID PULSE TRAIN HAVE BEEN COUNTED; RESET CIRCUIT MEANS COUPLED TO SAID DIGITAL COUNTER MEANS FOR SELECTIVELY SETTING AND RESETTING SAID COUNTER MEANS IN ACCORDANCE WITH A CONTROL SIGNAL; SELECTOR MEANS, FOR DETERMINING A DESIRED WIDTH OF BOARD TO BE CUT BY SAID SAWMILL, COUPLED TO SAID DIGITAL COUNTER MEANS FOR ENCODING SAID COUNTER MEANS TO PRODUCE SAID FIRST OUTPUT SIGNAL WHEN SAID FIRST PREDETERMINED NUMBER OF PULSES ARE COUNTED AND SAID SECOND OUTPUT SIGNAL WHEN SAID SECOND PREDETERMINED NUMBER OF PULSES ARE COUNTED; SWITCH MEANS, COUPLED BETWEEN SAID COUNTER MEANS, SAID PRIME MOVER MEANS AND ALSO TO SAID RESET CIRCUIT AND BEING RESPONSIVE TO SAID FIRST OUTPUT SIGNAL TO TRANSMIT A DECELERATE COMMAND SIGNAL TO SAID PRIME MOVER MEANS AND BEING RESPONSIVE TO SAID SECOND OUTPUT SIGNAL TO TRANSMIT A STOP COMMAND SIGNAL TO SAID PRIME MOVER MEANS AS DETERMINED BY THE TIME DELAY OCCURRING BETWEEN SAID FIRST AND SAID SECOND PREDETERMINED NUMBER OF PULSES COUNTED BY SAID DIGITAL COUNTER MEANS; AND CONTROL MEANS COUPLED TO SAID SWITCH MEANS APPLYING A SET SIGNAL THERETO WHEREUPON SAID SWITCH MEANS REMOVES SAID DECELERATE AND SAID STOP COMMAND SIGNAL FROM SAID PRIME MOVER MEANS AND TRANSMITS A FIRST AND A SECOND FORWARD SPEED COMMAND SIGNAL TO SAID PRIME MOVER MEANS AND TRANSMITS SAID CONTROL SIGNAL TO SAID RESET CIRCUIT FOR SELECTIVELY SETTING AND RESETTING SAID DIGITAL COUNTER MEANS. 